Evidence for the absolute conformational specificity of the intestinal H+/peptide symporter, PEPT1.
This study was initiated to determine whether the intestinal H+/peptide symporter PEPT1 differentiates between the peptide bond conformers of substrates. We synthesized a modified dipeptide where the peptide bond is replaced by the isosteric thioxo peptide bond. The Ala-Pro derivative Ala-psi[CS-N]-Pro exists as a mixture of cis and trans conformation in aqueous solution and is characterized by a low cis/trans isomerization rate. The compound was recognized by PEPT1 with high affinity. The Ki value of Ala-psi[CS-N]-Pro for the inhibition of the uptake of radiolabeled glycylsarcosine in Caco-2 cells was 0.30 +/- 0.02 mM, determined in solution with 96% trans conformation. In contrast, the Ki value was 0.51 +/- 0.02 mM when uptake media with 62% trans conformer were used. We conclude that only the trans conformer interacts with the transport system. From our data, a significant affinity of the cis conformer at PEPT1 cannot be derived. In a second approach, conformer-specific uptake of Ala-psi[CS-N]-Pro was studied by analyzing the intracellular content of Caco-2 cells following transport as well as the composition of the extracellular medium using capillary electrophoresis. The percentage of trans conformer that was 62% in the uptake medium increased to 92% inside the cells. This is the first direct evidence that an H+/peptide cotransport system selectively binds and transports the trans conformer of a peptide derivative.
Brandsch
M
M
Biozentrum,Martin-Luther-University Halle-Wittenberg, D-06120 Halle, Germany.
Thunecke
F
F
Küllertz
G
G
Schutkowski
M
M
Fischer
G
G
Neubert
K
K
D001692:Biological Transport / Q000502:physiology; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000737:chemistry; D004151:Dipeptides / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D019075:Electrophoresis, Capillary; D006801:Humans; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D000074011:Peptide Transporter 1; D027981:Symporters
D002352:Carrier Proteins; D004151:Dipeptides; D000074011:Peptide Transporter 1; C082186:SLC15A1 protein, human; D027981:Symporters; C004194:glycylsarcosine